Backspace causing threads to disappear

I have my zimbra set up with conversation view. My inbox was open, and I received an IM, so began responding to it. At some point, the cursor went back to the inbox instead of the IM. Without noticing it, I clicked backspace 6-8 times, which removed 6-8 entire conversation threads from my inbox. They don't appear to be in my trash, my drafts, or any of my other folders.
I don't specifically remember the subjects or senders, and so I have had extremely limited success "searching" for them. The ones that I was able to find through a search appear to have been deleted from the trash with that one little keystroke, but were able to be moved back to my inbox.

Any suggestions on how to find the remainder of my threads? Also, this massive deletion seems like a lot of action from just the backspace button. Is this a bug?